Integrated circuits (ICs) are typically housed within a plastic or ceramic package. The packages have leads or surface pads that are soldered to a printed circuit board. The circuit board and package are often located within an enclosed computer chassis that contains other circuitry associated with the computer system such as peripherals, memory cards, video cards, power supplies, etc.
It is desirable to have a high rate of heat transfer from the IC package in order to maintain the temperatures of the IC within safe operating limits. Modern microprocessors typically employ millions of transistors in internal circuitry that require some type of cooling mechanism, otherwise, excessive temperatures may affect the performance of the circuit and cause permanent degradation of the device. Hence, as the performance of integrated circuits continue to expand, the need to provide more efficient, reliable and cost effective heat removal methods has become increasingly important in the design of computer system enclosures and particularly in small general purpose computer systems, such as laptop and notebook computers.
A number of prior art methods have been used to remove heat from heat generating components located within the confines of a computer system enclosure. For example, the method of cooling integrated circuit devices within notebook computers has evolved from the simple attachment of a finned heat sink to the top surface of the device, to the development of finned heat sinks having integral fans. More recent developments have included the use of large, flat heat spreading plates. In such applications, the integrated circuit (generally, the CPU) is directly or indirectly attached to a metal plate having a large thermal mass and a large heat transfer surface area. In some instances, the integrated circuit device is thermally coupled to the heat spreading plate by a heat pipe or other low resistance thermal path.
Some prior art heat removal systems utilize the computer keyboard as the system heatsink structure. As shown in FIG. 1, a typical computer keyboard 100 includes a support plate 102 onto which is mounted a printed circuit board 104 and a plurality of keys 106 upon which a user may strike to input data into the computer. Generally, the keyboard support plate 102 is configured as one of the largest metallic members within a portable computer and is therefore chosen as a heatsink in some heat removal system designs.
FIG. 2 illustrates a prior art heat removal system 200 located within a portable computer. Heat removal system 200 includes a circular heat pipe 110 that transfers heat away from an integrated circuit device 120 to a heat spreading plate 116 that is attached to the keyboard support plate 102. Device 120 is generally attached directly to a copper or aluminum mounting plate 122 by a thermal adhesive. Heat pipe 110 includes an evaporator portion 112 and a condenser portion 114. Evaporator portion 112 is typically embedded in mounting plate 122. Keyboard support plate 102 includes a clamp portion 118 for receiving the condenser portion 114 of heat pipe 110.
U.S. Pat. No. 5,568,360 also describes a heat removal system for a portable computer wherein the keyboard support plate serves as the system heat sink.
A common problem associated with these prior art heat removal systems is that the stacking height of the system components impose a design restraint on the thickness of the computer. These systems are also difficult to assemble. In addition, since the heat pipes of the prior art heat removal systems are attached to the keyboard support plate along discrete locations, the heat flux distribution across the surface of the keyboard tends to be non-uniform. This results in the keyboard being hotter in locations adjacent to the heat pipe and cooler at points located away from the heat pipe. This reduces the efficiency of the heat removal system. Moreover, the existence of hot spots along the surface of the keyboard can cause discomfort to the user.
What is needed then is an apparatus which solves the aforementioned problems associated with cooling internal electronic circuits located within portable consumer electronic and computer devices. Particularly, what is needed is a highly efficient cooling system that is conformable to the size restrictions imposed by small form factor and thin profile electronic devices, such as, for example, notebook computers.